U.S. Pat. No. 6,637,107 discloses a method of manufacturing a variator disc having a concave race on one of its faces to be engaged by rollers and a splined central bore for engaging a splined shaft. This method comprises the steps of:
forming a concave race with a machining allowance on a face of an annular blank;
forming said splined bore through the blank providing the race;
heat-treating the blank to harden it, and
in a condition in which the blank is retained on the shaft which engages the splined bore after heat-treating the blank, performing a finishing step on an outer periphery of said disc by using the shaft as a reference for the finishing. The finishing of the race is then performed using the outer periphery as a reference for machining. A variant of the method provides that, after the heat-treatment, the finishing of the flanks of the grooves is performed by means of a broach, and then the race is finished by using the sides of the grooves as a reference for machining.
DISCLOSURE OF INVENTION
The present invention is directed to manufacturing a toroidal disc which provides a race machined with the highest possible accuracy.
This object is achieved, in accordance with the present invention, by a manufacturing method comprising steps including:
obtaining a steel disc blank of steel with a machining allowance, the disc blank having a first face with a concave race, a second face opposite the first face, a through central bore extending between the first and the second faces, and an outer peripheral edge;
heat treating the disc blank;
turning the concave race on a lathe;
wherein the phase of turning the concave race is preceded by a phase of turning the bore, thereby obtaining at least a turned cylindrical portion of the bore, and
the phase of turning the concave race is carried out while the disc blank is locked on the lathe by means of jaws which engage the turned cylindrical portion, using this turned cylindrical portion as a reference surface for turning the concave race.
Preferred embodiments of the invention are defined in the dependent claims.